A LevelBiologyOCRExam Questions5. Communication, Homeostasis & Energy5.5 Plant & Animal Responses

Plant & Animal Responses (OCR A Level Biology)

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5.5 Plant & Animal Responses

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5.5 Plant & Animal Responses

1a
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Students investigated the effect of light on the growth of garden cress seedlings.

  • A total of 120 seedlings were divided into 2 groups of 60.
  • Group A was grown in darkness for 2 days.
  • Group B was grown for 1 day in darkness and then for 1 day in white light using the set‐up shown in Fig. 3.1.q3-paper-3-nov-2020-ocr-a-level-biology

Fig. 3.1

The results of the students’ experiment are shown in Tables 3.1 and 3.2.

Group Mean length (mm) Mean mass (μg)
stem root stem root
A 13 18 102 60
B 25 23 160 120

Table 3.1

Direction of growth in Group B Number of seedlings
stem root
Away from light 2 29
Neither away from nor towards light 3 20
Towards light 55 11

Table 3.2


(i) 

Describe and explain the results shown in Tables 3.1 and 3.2.

[6]

(ii)
The students wanted to test whether there was a significant difference between the stem lengths of the seedlings in Group A and the seedlings in Group B.

State the name of the most appropriate statistical test for the students to use.

 [1]

(iii)
Justify your choice of statistical test given in part (ii).

 [1]

(iv)
Table 3.2 records the direction of growth as:

  • away from light
  • neither away from nor towards light
  •  towards light.
The students used the chi‐squared test to determine whether the direction of root growth was significantly different from their expectations.

Their null hypothesis was:

There is no difference between the expected direction of root growth and the observed direction of root growth.

The calculated chi‐squared value was 8.10.

The students compared their chi‐squared value of 8.10 to the values in Table 3.3.

Degrees of
freedom		 Probability (p)
0.10 0.05 0.01
1 2.71 3.84 6.64
2 4.60 5.99 9.21
3 6.25 7.82 11.34
4 7.78 9.49 13.28
5 9.24 11.07 15.09

Table 3.3

What can the students conclude about their results based on a chi‐squared value of 8.10?

[3]

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1b
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The solution in which the seedlings were grown contained various dissolved ions.

The table below lists two of the functions of these ions in the seedlings.

Complete the table below with the formula of each ion.

Function Formula of ion
Supplies elements that form part of the
structure of amino acids and nucleotides		  
Forms part of the structure of DNA and
phospholipids		  

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1c
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The students also investigated the effect of plant hormone concentration on root growth.

(i)
State the name of a plant hormone that would be expected to affect root growth. 
[1]
(ii)
In the investigation, the students controlled light, temperature and mineral concentration.

State one other factor that the students should have controlled in this investigation.
 [1]

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1d
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The growth of plant roots is thought to be controlled by specialised cells called statocytes.

One hypothesis for how a statocyte controls root growth involves small organelles called amyloplasts and is shown in Fig. 3.2.

q3d-paper-3-nov-2020-ocr-a-level-biology

Fig. 3.2

What can you conclude from the information in Fig. 3.2 about how a statocyte controls root growth?

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2a
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Gibberellin causes stem elongation in plants.

Fig. 17.1 shows the effect of gibberellin on cabbage plants.q17-paper-1-june-2019-ocr-a-level-biology

Fig. 17.1

Gibberellin causes an increase in the distance between the leaves on the stem, which is known as the internodal length.

Explain why gibberellin is classed as a plant hormone.

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2b
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A scientist carried out an investigation into the effect of gibberellin on cabbage plants.

The scientist applied a range of volumes of gibberellin and measured the rate of increase of internodal length over 30 days.

Table 17 shows the scientist’s results.

Volume of gibberellin
applied
(x10−3 cm3 kg−1 day−1)		 Rate of increase of
internodal length
(mm day−1)
0.0 1
0.2 1
0.4 2
0.6 4
0.9 22
1.2 47
1.4 48
1.8 49
1.9 50
2.0 50

Table 17

(i)
Plot the results from Table 17 as a suitable graph.q17b-2-paper-1-june-2019-ocr-a-level-biology

[4]

(ii)
Gibberellin causes an increase in internodal length.

State one other role of gibberellin in plants.

[1]

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2c
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A student carried out chemical tests on cabbage leaves to investigate which molecules were present.

The student’s method was as follows:

  • Add 50cm3 of distilled water to 2 large cabbage leaves and blend into a smooth liquid using a food mixer.
  • Place 1cm3 of the blended cabbage leaf liquid into 5 test tubes:
    – Tube 1: Add 5 drops of biuret reagent and mix.
    – Tube 2:

    Add 2cm3 of Benedict’s solution, mix, then place tube into a water bath for 5min. Remove and cool.
    – Tube 3: Add 2 drops of iodine solution and mix.
    – Tube 4:

    Add 2cm3 of ethanol and mix. Then add 2cm3 of distilled water and mix.
    – Tube 5:

    Insert a glucose test strip into the liquid then compare the colour to the colour chart provided (see Fig. 17.2 below).

Colour comparison chart for glucose test strip
fig-17-insert-paper-1-june-2019-ocr-a-level-biologyFig. 17.2
(i)
Name a type of food molecule that the student will not be able to detect using these chemical tests.
[1]

(ii)
The table below is a summary of some of the student’s findings.

Complete the table by writing in the missing observations and conclusions.

Tube Observation Conclusion
1 ......................................... Protein present
2 Yellow colour ................................................................
3 Pale brown colour ................................................................
4 ......................................... Fat present
5 ......................................... Glucose concentration small (15mg dm−3)


[2]

(iii)
The student then used a colorimeter to measure the absorbance of the contents of Tube 2.

Explain how the use of a colorimeter could improve the student’s conclusion.
[1]

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3a
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Gestational diabetes is a medical condition that affects pregnant women. It results in high levels of glucose in the blood, even though the woman produces normal levels of insulin.

(i)
Gestational diabetes is most similar to which other type of diabetes?
Explain your answer.
[2]
(ii)
Suggest two ways a woman with gestational diabetes can manage her condition.
[2]

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3b
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Skeletal muscle is one of the main tissues where glucose is removed from the blood in response to insulin.

(i)
Name the other tissue.
[1]
(ii)
Explain why glucose is required for the contraction of skeletal muscle.
[3]

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3c
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During late pregnancy, women find ventilation more difficult, as the developing foetus reduces the volume of the thorax. This can lead to tiredness and difficulty breathing.

A student used a spirometer to measure ventilation in a woman who was 36 weeks pregnant.

Fig. 16.1 shows the trace produced.

q16c-paper-1-june-2018-ocr-a-level-biology

Fig. 16.1 

Mean oxygen uptake rate at rest in women is around 0.020 dm cubed space straight s to the power of negative 1 end exponent

Using these data, the student made the following conclusion:


    My data show that being pregnant reduces rate of oxygen uptake by up to 20%


Evaluate this claim, using the data in Fig. 16.1.

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4a
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Plant hormones affect the growth of plant tissues in different ways.

One such effect is to promote the formation of seedless fruit.

Cytokinins are a group of plant hormones.

A commercial plant hormone firm carried out research into three different cytokinins: kinetin, zeatin and diatin.

The firm investigated the effect of adding different volumes of each cytokinin on the production of seedless fruit.

The cytokinins were sprayed on the flowers of different plants. Over time, the mass of seedless fruits produced by the plants was measured.

Fig. 21 is a summary of their results.

q21-paper-1-june-2017-ocr-a-level-biology

Fig. 21

On the basis of these results, the firm decided to use diatin in their new plant spray.

The firm made the following claim on their packaging:

Diatin is scientifically proven to cause production of seedless fruit when applied to flowers.

Evaluate the firm’s claim, using the evidence in Fig. 21.

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4b
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Another response affected by plant hormones is phototropism.
A student completed an investigation into phototropism in cress seeds.
This was the method used:

  • Place 50 cress seeds (Lepidium sativum) on a sterile paper towel in a petri dish.
  • Water with 10cm3 of distilled water.
  • Repeat for 3 different sets of seeds:
    • Set 1 is placed in a box to prevent light shining on the seeds.
    • Set 2 is placed in a box with light from above only.
    • Set 3 is placed in a box with light from the right hand side only.
  • Keep all 3 sets at 25°C.
  • After 72 hours, remove 20 of the seedlings from each set and count how many have bent.

Identify two limitations of the student’s method.

For each limitation, explain how it limits the validity of conclusions that can be drawn and suggest an improvement that would improve the validity of conclusions made.

limitation 1: .........................................................

explanation: .........................................................

improvement: .........................................................

limitation 2: .........................................................

explanation: .........................................................

improvement: .........................................................

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5a
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Multiple sclerosis (MS) is an autoimmune disease that damages the nervous system.

(i)
Suggest how the immune system causes damage to the nervous system.
[2]

(ii)
Fig. 5 shows three neurones of different sizes from a person with MS.
micrograph
Fig. 5

One of the neurones has been affected by MS.

MS causes changes to neurones, which reduce the speed at which nervous impulses are conducted.

Using information from Fig. 5, what can you conclude about how MS causes a reduction in the speed of nervous impulses?
[2]

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5b
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Guillain–Barré syndrome is another autoimmune condition in which neurones are damaged and the rate of nervous impulses is reduced.

MS affects the central nervous system.

Guillain–Barré syndrome affects the peripheral nervous system.

(i)
Suggest two symptoms of MS that might not be present in people with Guillain–Barré syndrome.

Explain your answers.
[2]
(ii)
Multiple sclerosis and Guillain–Barré syndrome both cause muscle weakness and loss of muscle function.

Suggest and describe how the function of neuromuscular junctions will be affected by multiple sclerosis and Guillain–Barré syndrome.
[2]

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6
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Herbicides work in a number of different ways.

(i)

Some herbicides, known as phenoxy herbicides, mimic the action of the auxin, indoleacetic acid (IAA).

What is the normal action of IAA in plant cells?

[1]

(ii)

The herbicide atrazine works by disabling plastoquinone, one of the proton pumps in photosystem II.

Explain how atrazine would kill a susceptible plant.

[5]

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